Atom interferometric sensors and quantum information processors must maintain coherence while the evolving quantum wavefunction is split, transformed and recombined, but suffer from experimental inhomogeneities and uncertainties in the speeds and paths of these operations. Several error-correction techniques have been proposed to isolate the variable of interest. Here we apply composite pulse methods to velocity-sensitive Raman state manipulation in a freely-expanding thermal atom cloud. We compare several established pulse sequences, and follow the state evolution within them. The agreement between measurements and simple predictions shows the underlying coherence of the atom ensemble, and the inversion infidelity in an 80 micro-Kelvin atom cloud is halved. Composite pulse techniques, especially if tailored for atom interferometric applications, should allow greater interferometer areas, larger atomic samples and longer interaction times, and hence improve the sensitivity of quantum technologies from inertial sensing and clocks to quantum information processors and tests of fundamental physics

To search for the temporal variation of the fundamental constants one needs to know dependence of atomic transition frequencies on these constants. We study the dependence of the hyperfine structure of atomic s-levels on nuclear radius and, via radius, on quark masses. An analytical formula has been derived and tested by the numerical relativistic Hartree-Fock calculations for Rb, Cd + , Cs, Yb + and Hg + . The results of this work allow the use of the results of past and future atomic clock experiments and quasar spectra measurements to put constrains on time variation of the quark masses.

Sympathetic cooling of trapped ions through collisions with neutral buffer gases is critical to a variety of modern scientific fields, including fundamental chemistry, mass spectrometry, nuclear and particle physics, and atomic and molecular physics. Despite its widespread use over four decades, there remain open questions regarding its fundamental limitations. To probe these limits, here we examine the steady-state evolution of up to 10 barium ions immersed in a gas of three-million laser-cooled calcium atoms. We observe and explain the emergence of nonequilibrium behaviour as evidenced by bifurcations in the ion steady-state temperature, parameterized by ion number. We show that this behaviour leads to the limitations in creating and maintaining translationally cold samples of trapped ions using neutral-gas sympathetic cooling. These results may provide a route to studying non-equilibrium thermodynamics at the atomic level.

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We report the 1-D cooling of 85 Rb atoms using a velocity-dependent optical force based upon Ramsey matter-wave interferometry. Using stimulated Raman transitions between ground hyperfine states, 12 cycles of the interferometer sequence cool a freely-moving atom cloud from 21 µK to 3 µK. This pulsed analog of continuous-wave Doppler cooling is effective at temperatures down to the recoil limit; with augmentation pulses to increase the interferometer area, it should cool more quickly than conventional methods, and be more suitable for species that lack a closed radiative transition.The laser cooling of atomic gases has revolutionized experimental atomic physics [1] and raised the prospect of a range of atomic quantum technologies [2,3]. However, traditional Doppler cooling [4,5] relies upon the velocity-dependence of a single narrow radiative transition, and spontaneous emission to reset the atomic state. The cooling force is limited to a half photon-impulse per excited-state lifetime and, as many impulses are needed, requires a transition that can be closed by a few repump lasers. Doppler cooling has thus so far been limited to a handful of atomic elements and molecules [6][7][8][9].In [10], Weitz and Hänsch proposed a mechanism that could extend laser cooling to a wider range of species, by replacing the continuous wave (CW) excitation of conventional Doppler cooling with the broadband laser pulses of Ramsey matter-wave interferometry, and interleaving inversion pulses to eliminate the dependence upon the internal state energies. The interference signal, and hence the impulse imparted, were thus determined only by the particle's kinetic energy; manifold transitions could be accessed and, while spontaneous emission remained the entropy-removing mechanism, various schemes [11][12][13] could increase the impulse per spontaneous event. With a drive towards efficient pulsed schemes for molecular cooling [14][15][16] supported by improved mode-locked laser technologies, interferometric cooling appears a promising and flexible tool.The idea of a pulsed Ramsey analog to CW Doppler cooling has until now remained untested. In this letter, we report the first experimental demonstration of 1-D interferometric cooling of a cloud of already ultracold Rb atoms. Our long-lived quasi-two-level system, comprising the two 5S 1/2 ground hyperfine states of 85 Rb between which we drive stimulated Raman transitions, in principle allows cooling to the recoil limit, and we show that with just 12 cycles of the interferometric cooling sequence the atom cloud is cooled from 21 ± 2 µK to 3.2 ± 0.4 µK. Relaxation after each cycle is achieved by rapid pumping and decay of the single-photon 5S 1/2 -5P 3/2 transition, and the cooling rate is therefore limited mainly by the time needed for interferometric resolution of the different velocity classes.The Raman interferometric cooling mechanism is as follows. Two π/2 laser pulses, separated by a dwell time τ , act upon a two-level atom |Ψ = c 1 |1 + c 2 |2 as the beamsplitter and combiner of a R...